Recent studies have demonstrated the ease and utility of displaying foreign peptides on the surface of filamentous bacteriophages for applications ranging from screening of epitope libraries to the production of vaccines. This project will be aimed at determining the structure of a variety of these peptide antigens as they are displayed on the surface of bacteriophage M13. The proposed collaboration is between the first laboratory to report the production of bacteriophage carrying antigen epitopes in gene 8 and the laboratory that has recently determined the three-dimensional structure of M13. Structural studies will utilize fiber diffraction studies of engineered virus particles to determine the conformation of the peptides displayed on the virion surface. Structural analysis of the resulting fiber patterns will be a straightforward extension of the work on native M13 and isomorphous derivatives of that virus recently completed. These results will provide important information about the structure of antigenically active peptides and, consequently, should contribute significantly to the design of engineered vaccines.